Queensland is in the grip of another extraordinary flood crisis, as cities and towns across the state go under.

Three people are dead and Brisbane residents are being warned to brace for the worst as 3600 residential properties and 1250 businesses are expected to experience flooding later today.

Six tornadoes that hit the Mackay and Bundaberg regions caused damage to hundreds of homes. More than 100,000 homes and businesses lost power in Ipswich, Moreton Bay, Logan, parts of the Gold Coast and Brisbane.

Experts describe the flooding and tornadoes battering the east coast as the worst they have seen in 30 years.

Stressing that the situation facing Brisbane was not as bad as it was in 2011, Queensland premier Campbell Newman told residents in the firing line that now was the time to "take action", with many opting to move their possessions and seek higher ground.

Dramatic rescues are under way in Bundaberg, where the city's worst flood on record has left dozens of people trapped on rooftops.

At least 1200 properties are already flooded in Bundaberg, with fears that could reach 2000.

The communities of Gympie and Maryborough are also under water.

There is also a major flood crisis developing in the Lockyer Valley, where 19 lives were lost in the state's 2011 floods.

So far, three flood deaths have been confirmed: an 81-year-old man whose body was pulled from the water near Bundaberg, a 27-year-old wheelchair-bound man who was found near Gympie, and a male motorcyclist, who was swept off the road at Greenbank, near Ipswich.

Rivers are expected to peak tonight, noon tomorrow and again on Wednesday.

In Bundaberg, entire suburbs have been evacuated but some people waited too long and about 30 were stranded on rooftops. Newman said attempts to rescue them were being hampered by "very swift, very dangerous water" flowing in the area.

Six winch cable helicopters had been deployed with the support of army Black Hawks, he said.

The situation in the city is now so bad that police are advising people trapped in homes in north Bundaberg to seek refuge on the roof.

"If your house is currently inundated with water and you require rescuing, you are either to make your way to the roof if safe - I repeat - if safe," Senior Sergeant Grant Marcus said in an urgent public alert.

"Alternatively find a way by which you can hail rescue helicopters which are currently hovering over your area."

There were higher than expected falls in waterways that feed into the Brisbane River, downstream of the protective Wivenhoe dam, overnight.

"Queensland is facing a very serious challenge right now," Newman said, with Laidley, Lockyer Creek and Bremer River standing as a "grave concern this morning".

"If their properties are on [the flood maps] I must say this morning you must take action."

The premier was expected to visit the Lockyer Valley today, where evacuation orders are in place due to flooding in Lockyer Creek and Laidley Creek.

Australian prime minister Julia Gillard has offered her condolences after three people died in Queensland's wild weather, saying the floods had ''broken a lot of hearts''.

Gillard, touring bushfire-affected parts of Victoria, said nature was challenging the nation but people would ''get through this'' by pulling together.

The comments came as opposition leader Tony Abbott dropped into an State Emergency Service (SES) depot in Brisbane to fill sandbags as the city braced for flooding after days of wild weather.

Deputy prime minister Wayne Swan, meanwhile, has Ipswich city, west of Brisbane, where residents have also been put on flood alert.

Gillard said the wild weather had ''broken a lot of hearts'' and believed the current events would be a particularly difficult time psychologically for residents in the Lockyer Valley.

''Given everything that has happened in Queensland over the last two years this is a particularly heart-breaking time for people.

''Whether it's bushfires, whether it's floods we are being challenged by nature, but we are a strong and smart nation and we will get through this like we always do, by pulling together.''

Gillard said she had spoken to Newman and offered to assist.

So far, the Australian Defence Force had provided Black Hawks to help flood-affected communities.

Gillard offered her condolences to the friends and family of three people who had lost their lives and urged people to stay safe by taking precautions, listening to warnings and not entering flood waters.

A decision about when to visit Queensland would be made, she said, as she wanted to find a time that did not distract from local efforts.

FLIGHTS CANCELLED

All flights in and out of the Gold Coast have been suspended until further notice, Australia's major airlines have reported.

However, flights could resume if the weather improves this afternoon.

Brisbane Airport remains open but there are many delayed and cancelled flights across all airlines heading out of the city.

Leonie Vandeven from Brisbane Airport Corporation said customers should check the status of their flights online with their respective airlines, as call centres were experiencing considerable delays.

CLAIMS ALREADY AT $43 MILLION

Insurance claims from the latest floods have already topped $43 million, as river levels continue to rise in large parts of the state.

Early this afternoon about 5050 claims had been lodged relating to losses from the major rain event now affecting Queensland and New South Wales, said Campbell Fuller, general manager for communications at the the Insurance Council of Australia.

The total claimed losses are likely to be reach $50 million by mid week, he said.

OSWALD MOVES SOUTH

As water poured into homes and businesses in Queensland, the effects of the weather pattern delivered by ex-tropical cyclone Oswald began to shift south, with a deluge forecast for Sydney.

The weather bureau issued a severe weather warning for parts of NSW, with heavy rainfall and winds of up to 140 kilometres an hour expected.

Up to 300 millimetres of rain could fall in areas of Sydney over 24 hours from this morning, the bureau said.

EXPECTED PEAKS

Newman said the town of Gympie was expected to see a flood peak of 21 metres today, higher than the 2011 mark of 19.45m.

This morning the Burnett River was at 8.7m and rising, with nine evacuation centres established in the city he said.

The Bremer River in Ipswich is expected to peak above the January 2011 flood level of 11.7m by noon today (2pm, NZ time).

The Mary River at Gympie is expected to peak at 21m, higher than the 2011 level of 19.45m.

Meanwhile Rockhampton is preparing for a "very significant" flood event, with a flood peak moving down the river over the coming days.

Newman said the full impact would be be felt at the weekend.

Flood waters are also rising in the Gympie CBD, with suburbs in Maryborough already flooding and preparations underway two evacuation centres established.

Newman also announced a Queensland Floods Appeal, to be run by the Red Cross. Donations can be made through their website.

CLEAN-UP STARTS

And while the situation was still unfolding across the state, Newman said the clean-up in some districts had already begun and called for support from the federal government.

SES crews received 1800 calls for help in the 24 hours up to 4am Monday (6am, NZ time), with unforgiving winds bringing down trees and power lines.

About 1000 of those calls were from the southeast, with residents needing assistance sandbagging against floods, fixing leaky roofs and removing fallen power lines.